Strategies for Determining the Cascade Rate in MHD Turbulence: Isotropy, Anisotropy, and Spacecraft Sampling
Strategies for Determining the Cascade Rate in MHD Turbulence: Isotropy, Anisotropy, and Spacecraft Sampling
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DOI：
10.3847/1538-4357/ac8f90
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发表时间：
2022-09
期刊：
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通讯作者：
Yanwen Wang;R. Chhiber;S. Adhikari;Yan Yang;R. Bandyopadhyay;M. Shay;S. Oughton;W. Matthaeus;M. Cuesta
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作者：
Yanwen Wang;R. Chhiber;S. Adhikari;Yan Yang;R. Bandyopadhyay;M. Shay;S. Oughton;W. Matthaeus;M. Cuesta
精确的法律评估级联率，追溯到柯尔莫哥洛夫“4/5”定律，已被扩展到许多系统的利益，包括磁流体（MHD），可压缩流的磁流体和普通流体类型。应当理解，实施方式可能受到可用数据的数量和湍流对称性的缺乏的限制。评估这种三阶（或Yaglom）关系的准确性和可行性最有效的方法是检查增量形式的冯卡门-豪沃思方程，这是一个框架，三阶定律是作为渐近近似导出的。使用这种方法，我们研究的内容不可压缩MHD的三阶法律的一些细节。最简单的版本依赖于各向同性的假设和存在一个定义良好的惯性范围，而相关的程序将相同的想法推广到任意旋转对称。从这些法律的基础上几个采样和拟合策略的耗散率获得正确和准确的值的条件进行了研究，使用模拟结果。我们处理的问题是特别相关的采样太阳风湍流的一个或多个航天器。
Exact laws for evaluating cascade rates, tracing back to the Kolmogorov “4/5” law, have been extended to many systems of interest including magnetohydrodynamics (MHD), and compressible flows of the magnetofluid and ordinary fluid types. It is understood that implementations may be limited by the quantity of available data and by the lack of turbulence symmetry. Assessment of the accuracy and feasibility of such third-order (or Yaglom) relations is most effectively accomplished by examining the von Kármán–Howarth equation in increment form, a framework from which the third-order laws are derived as asymptotic approximations. Using this approach, we examine the context of third-order laws for incompressible MHD in some detail. The simplest versions rely on the assumption of isotropy and the presence of a well-defined inertial range, while related procedures generalize the same idea to arbitrary rotational symmetries. Conditions for obtaining correct and accurate values of the dissipation rate from these laws based on several sampling and fitting strategies are investigated using results from simulations. The questions we address are of particular relevance to sampling of solar wind turbulence by one or more spacecraft.